Hormone secretion by pituitary adenomas is characterized by increased disorderliness and spikiness but more regular pulsing

High-resolution daily profiles of tissue adrenal steroids by portable automated collection

Rhythms are intrinsic to endocrine systems, and disruption of these hormone oscillations occurs at very early stages of the disease. Because adrenal hormones are secreted with both circadian and ultradian periods, conventional single-time point measurements provide limited information about rhythmicity and, crucially, do not provide information during sleep, when many hormones fluctuate from nadir to peak concentrations. If blood sampling is attempted overnight, then this necessitates admission to a clinical research unit, can be stressful, and disturbs sleep. To overcome this problem and to measure free hormones within their target tissues, we used microdialysis, an ambulatory fraction collector, and liquid chromatography-tandem mass spectrometry to obtain high-resolution profiles of tissue adrenal steroids over 24 hours in 214 healthy volunteers. For validation, we compared tissue against plasma measurements in a further seven healthy volunteers. Sample collection from subcutaneous tissue was safe, well tolerated, and allowed most normal activities to continue. In addition to cortisol, we identified daily and ultradian variation in free cortisone, corticosterone, 18-hydroxycortisol, aldosterone, tetrahydrocortisol and allo-tetrahydrocortisol, and the presence of dehydroepiandrosterone sulfate. We used mathematical and computational methods to quantify the interindividual variability of hormones at different times of the day and develop "dynamic markers" of normality in healthy individuals stratified by sex, age, and body mass index. Our results provide insight into the dynamics of adrenal steroids in tissue in real-world settings and may serve as a normative reference for biomarkers of endocrine disorders (ULTRADIAN, NCT02934399).

The biochemical diagnosis of acromegaly: revising the role of measurement of IGF-I and GH after glucose load in 5 questions

INTRODUCTION

Acromegaly is a rare disorder characterized by the excessive secretion of growth hormone (GH), mostly caused by pituitary adenomas. While in full-blown cases the diagnosis is easy to establish, milder cases are more challenging. Additionally, establishing whether full cure after surgery is reached may be difficult.

AREAS COVERED

In this article, we will review the challenges posed by the variability in measurements of GH and its main effector insulin-like growth factor I (IGF-I) due to both biological changes, co-morbidities, and assays variability.

EXPERT OPINION

Interpretation of GH and IGF-I assays is important in establishing an early diagnosis of acromegaly, in avoiding misdiagnosis, and in establishing if cure is achieved by surgery. Physicians should be familiar with the variables that affect measurements of these 2 hormones, and with the performance of the assays available in their practice.

The Processes of Anterior Pituitary Hormone Pulse Generation

More than 60 years ago, Geoffrey Harris described his "neurohumoral theory," in which the regulation of pituitary hormone secretion was a "simple" hierarchal relationship, with the hypothalamus as the controller. In models based on this theory, the electrical activity of hypothalamic neurons determines the release of hypophysiotropic hormones into the portal circulation, and the pituitary simply responds with secretion of a pulse of hormone into the bloodstream. The development of methodologies allowing the monitoring of the activities of members of the hypothalamic-vascular-pituitary unit is increasingly allowing dissection of the mechanisms generating hypothalamic and pituitary pulses. These have revealed that whereas hypothalamic input is required, its role as a driver of pulsatile pituitary hormone secretion varies between pituitary axes. The organization of pituitary cells has a key role in the modification of their response to hypophysiotropic factors that can lead to a memory of previous demand and enhanced function. Feedback can lead to oscillatory hormone output that is independent of pulses of hypophysiotropic factors and instead, results from the temporal relationship between pituitary output and target organ response. Thus, the mechanisms underlying the generation of pulses cannot be generalized, and the circularity of feedforward and feedback interactions must be considered to understand both normal physiological function and pathology. We describe some examples of the clinical implications of recognizing the importance of the pituitary and target organs in pulse generation and suggest avenues for future research in both the short and long term.

Feminization of Male Mouse Liver by Persistent Growth Hormone Stimulation: Activation of Sex-Biased Transcriptional Networks and Dynamic Changes in Chromatin States

Sex-dependent pituitary growth hormone (GH) secretory profiles-pulsatile in males and persistent in females-regulate the sex-biased, STAT5-dependent expression of hundreds of genes in mouse liver, imparting sex differences in hepatic drug/lipid metabolism and disease risk. Here, we examine transcriptional and epigenetic changes induced by continuous GH infusion (cGH) in male mice, which rapidly feminizes the temporal profile of liver STAT5 activity. cGH repressed 86% of male-biased genes and induced 68% of female-biased genes within 4 days; however, several highly female-specific genes showed weak or no feminization, even after 14 days of cGH treatment. Female-biased genes already in an active chromatin state in male liver generally showed early cGH responses; genes in an inactive chromatin state often responded late. Early cGH-responsive genes included those encoding two GH/STAT5-regulated transcriptional repressors: male-biased BCL6, which was repressed, and female-specific CUX2, which was induced. Male-biased genes activated by STAT5 and/or repressed by CUX2 were enriched for early cGH repression. Female-biased BCL6 targets were enriched for early cGH derepression. Changes in sex-specific chromatin accessibility and histone modifications accompanied these cGH-induced sex-biased gene expression changes. Thus, the temporal, sex-biased gene responses to persistent GH stimulation are dictated by GH/STAT5-regulated transcription factors arranged in a hierarchical network and by the dynamics of changes in sex-biased epigenetic states.

Combining Cadherin Expression with Molecular Markers Discriminates Invasiveness in Growth Hormone and Prolactin Pituitary Adenomas

Although growth hormone (GH)- and prolactin (PRL)-secreting pituitary adenomas are considered benign, in many patients, tumour growth and/or invasion constitute a particular challenge. In other tumours, progression relies in part on dysfunction of intercellular adhesion mediated by the large family of cadherins. In the present study, we have explored the contribution of cadherins in GH and PRL adenoma pathogenesis, and evaluated whether this class of adherence molecules was related to tumour invasiveness. We have first established, by quantitative polymerase chain reaction and immunohistochemistry, the expression profile of classical cadherins in the normal human pituitary gland. We show that the cadherin repertoire is restricted and cell-type specific. Somatotrophs and lactotrophs express mainly E-cadherin and cadherin 18, whereas N-cadherin is present in the other endocrine cell types. This repertoire undergoes major differential modification in GH and PRL tumours: E-cadherin is significantly reduced in invasive GH adenomas, and this loss is associated with a cytoplasmic relocalisation of cadherin 18 and catenins. In invasive prolactinomas, E-cadherin distribution is altered and is accompanied by a mislocalisation of cadherin 18, β-catenin and p120 catenin. Strikingly, de novo expression of N-cadherin is present in a subset of adenomas and cells exhibit a mesenchymal phenotype exclusively in invasive tumours. Binary tree analysis, performed by combining the cadherin repertoire with the expression of a subset of known molecular markers, shows that cadherin/catenin complexes play a significant role in discrimination of tumour invasion.

Pituitary Hormone Secretion Profiles in IGSF1 Deficiency Syndrome

BACKGROUND

Loss-of-function mutations in immunoglobulin superfamily member 1 (IGSF1) cause an X-linked syndrome of central hypothyroidism, macroorchidism, delayed pubertal testosterone rise, variable prolactin deficiency and variable partial GH deficiency in childhood. The clinical features and gene expression pattern suggest a pivotal role for IGSF1 in the pituitary, but detailed knowledge on pituitary hormone secretion in this syndrome is lacking. We therefore aimed to study the 24-hour pituitary hormone secretion in male patients with IGSF1 deficiency.

METHODS

We collected blood samples every 10 min for 24 h in eight adult male IGSF1-deficient patients and measured circulating TSH, prolactin and gonadotropins. Deconvolution, modified cosinor and approximate entropy analyses were applied to quantify secretion rates, diurnal rhythmicity and regularity of hormone release. Results were compared to healthy controls matched for age and body mass index.

RESULTS

Compared to healthy controls, IGSF1-deficient patients showed decreased pulsatile secretion of TSH with decreased disorderliness and reduced diurnal variation. Basal and pulsatile secretion of FSH was increased by over 200%, while LH secretion did not differ from healthy controls. We observed a bimodal distribution of prolactin secretion, i.e. severe deficiency in three and increased basal and total secretion in the other five patients.

CONCLUSION

The altered TSH secretion pattern is consistent with the previously hypothesized defect in thyrotropin-releasing hormone signaling in IGSF1 deficiency. However, the phenotype is more extensive and includes increased FSH secretion without altered LH secretion as well as either undetectable or increased prolactin secretion.